In the utilization of metal casting apparatus, it is necesary--for effective operation--to detect the rising speed of molten metal within a mold, and to adjust the rate-of-rise so that a desired rate is achieved.
Conventionally the rate-of-rise of molten metal in a mold is determined by an operator measuring the elapsed time between level marks on a container for the molten metal, as visually observed by the operator, or by timing between electrical contacts of the molten metal with a wire or wires maintained at known levels within the container. Such methods are often inaccurate due to the lack of precision inherent in such observations, and due to the inability to produce continuous and timely information which can be acted upon either manually or automatically to control the rate-of-rise as desired.
In U.S. Pat. No. 4,019,562, a proposal is made for the automatic control of the rate of increase of the level of molten metal within a mold utilizing a generator for generating a microwave Doppler signal, and hard-wired electronic circuitry for measuring the frequency of the Doppler signal. The circuitry employs the "phase-locked-loop" principle for frequency determination, and utilizes a reference pulse generator for that purpose.
According to the present invention, rate-of-rise of the level of a liquid is determined in a reliable, accurate, and flexible manner. The rate-of-rise is determined without hard-wired electronic circuitry. This is accomplished, according to the present invention, by undertaking the determination of the Doppler frequency entirely by computer analysis of a signal from a microwave mixer/detector. Analysis of the signal by digital logic procedures within the computer ensures reliability and accuracy of the rate-of-rise calculated, and additional provides flexibility for additional data usage.
The method and apparatus according to the present invention are applicable to many procedures and environments, being applicable whenever the accurate control of level and filling or emptying rate is important. One possible application is the determination of the rate-of-rise of molten metal in a mold. A preferred specific application for the invention is in the measurement and control of the rate-of-rise of liquid steel and the filling of ingot molds by the bottom-pour technique.
In the practice of the method according to the invention, the information generated by the computer processing may be used in a real-time or time average display in analog or digital form to permit an operator to adjust metal flow to closely approximate a desired rate. The information may be compared over time with a predetermined plan of desired rate versus time, and the instantaneous or time average difference from the target may be displayed to permit appropriate operator action. Information on both actual and rate comparison to a predetermined plan may be recorded over the period of an entire metal handling operation for subsequent analysis and display. By summsation of the measured rate of level change data over a time period the absolute level change, and thus the instantaneous actual level, can be measured for display and/or recording. Also, the information concerning actual rate of change and/or comparison with a predetermined target and/or absolute level change and/or instantaneous actual level, may be used as an input to a control system for automatic actuation of flow devices with the objective of obtaining the desired values.
The basic processing steps for determining the rate-of-rise include transmitting a microwave signal of controlled wave lengths to the surface of the molten metal in the mold, and detecting a mixed microwave signal comprised of a signal reflected from the surface of the metal in the mold, and a transmitted signal, and producing an analog output signal proportional to the mixed signal detected. The analog output signal is converted to a digital signal. Processing by the computer is then utilized to filter the digital signal, determine the noise level in the filtered signal, continuously analyze the digital signal level to determine the time difference between different detected turn-around times, analyze the digital signal to eliminate the effects of spurious multiple-reflection microwave signals and disturbances in the surface of the molten metal in the mold, and calculate the rate-of-rise of the surface of the molten metal in the mold.
Apparatus according to the present invention comprises a container adapted to have molten metal therein, a mold, means for passing molten metal from the container to the mold, and a rate-of-rise determining means. The rate-of-rise determining means includes a microwave generator, and a microwave antenna located above the mold (and connected to the generator by a waveguide) for transmitting microwaves to the surface of the molten metal in the mold. Such means further comprise a mixer/detector operatively connected to the antenna, and computer means operatively connected to the mixer/detector. Monitoring and/or controlling means are operatively connected to the computer means.
It is the primary object of the present invention to provide an improved method and apparatus for controlling, or facilitating the control of, the rate-of-rise of the level of molten metal in a mold. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.